THEORY OF OPERATION
Fuel Filters (Continued):
Fuel Injection Pump Filter - Also know as
"Last Chance Filter" or "Watchdog Filter" is
a ten-micron filter built onto the side of the
fuel injection pump.
Fuel Injection Pump:
The injection pump has three main functions.
First, it must meter, or measure, the amount
of fuel delivered to each injector nozzle. A
small amount of fuel is needed for an idling
engine, while a larger amount is needed for
high engine speed.
Second, it must pressurize the fuel delivered to the injector nozzles. The pump must be
capable of producing pressure higher than the nozzle opening pressure (greater than 3300 psi).
Third, it must distribute the fuel to the correct cylinder at the proper time.
The injection pump is a single plunger, constant stroke, distributor type. Although it is called
a single plunger type, the pump actually has a plunger in each of its two hydraulic distributing
heads. Each head supplies fuel to one bank of six cylinders. The pump is mounted between
the two cylinder banks and between the two fan towers. A shaft coupled to the accessory drive
gearing drives it. A timing advance unit is built into the injection pump drive to automatically
advance the injection timing at high engine speeds. The injection pump camshaft, gears, and
governor are lubricated by oil supplied from the engine main lubrication system.
Fuel Injection Nozzles and Tubes:
The fuel injection nozzle is a device that sprays fuel as a fine mist into the cylinder at the
proper time allowing efficient combustion. The injector nozzle must inject the fuel into the
combustion chamber in a pattern that produces maximum power and economy.
Twelve fuel injector nozzles, one per cylinder, are used to inject fuel into the combustion
Fuel injector tubes of equal length carry the fuel from the fuel injection pump to the nozzles.
Interconnecting fuel return lines provide a path for the return of excess fuel from the nozzles.
WP 0004 00-19